new to page, away from boyfriend, need advice please!

I'm new to this page, hi! I have an issue that I was wondering if anyone else is dealing with or has any advice to give me.
I have an amazing boyfriend who I have been with for ten months. He is loving, kind, patient, understanding, tall, handsome.. he is someone anyone would dream to have, and for some reason he was given to me.
Here is where things get complicated.
whenever I or he leaves for a vacation, I get intrusive thoughts. "You dont really love him" pounds on me morning and night, mainly in the morning and then only slightly for the rest of the day. I started getting these thoughts a week before I was going to leave him for six weeks, and eventually my hormones literally shut off and it was impossible for us to have any sort of intimacy together (making out, feeling each other, etc.)I started to not look forward to his texts, and when I would be with him during the last week of us together, I would have extremely bad anxiety when I was around him. I talked to my therapist and my mom, they both told me It was because I was leaving and that I would be back to normal when I got home.
this is the third week of me being away from him and nothing really has changed. My anxiety has gotten better, but now I'm on my time of the month and it is hell. Im on my fifth day but my anxiety still hasn't lessened. I fantasized about him, and for two or three seconds his friend replaced him in my mind and I became very upset and guilty feeling about that considering I would never in a million years cheat on him. Also, his friend is a major dick. I dont know if that counts as anything, but I thought i would bring that up. I will also add that during the week I was still with him while having the "you don't love him" thought, I also eventually went crazy because I started getting the thought "what if you developed a crush while you're down there?" I tried not to let that thought get to me, but anxiety is a dwelling disease. That drove me nuts until I came down here and realized I had nothing to worry about. I told my boyfriend about all of this and he somehow has been very understanding and still loving towards me.. Which makes me want to cry even more because I feel that he deserves someone much better than me, who wont have these thoughts.. he deserves the most perfect woman on the planet and I am nowhere near there. I am sixteen, if that adds to anything. i am in so much pain from this.. i would do anything to not feel like this. I want to be exactly what he deserves but I'm afraid I cant because of these thoughts.. he deserves so much better than this. If someone can please help me to redirect my thoughts and fight these things off, please help me.
thank you,
eve.